1. Field of the Invention
This invention relates to an improvement of probe pins for inspection of printed circuit boards and slip-on sockets thereof whereby a unit to inspect a printed circuit comprises a plurality of the probe pins pushed into holding openings formed on an insulated holding plate. For inspection of the circuit board, each probe pin contacts with each of the corresponding contacts of the printed circuit.
2. Description of the Related Art
FIG. 1 is a perspective view showing a conventional inspection unit for a printed circuit whereby an insulated holding plate 1 is provided with holding openings thereon into which a plurality of probe pins 2 for inspection are pushed to inspect the printed circuit. Guide flaps 3 provided in plurality around a group of the probe pins 2 guide the printed circuit substrate 4 into contact with the probe pin 2. Female connector 5 having a plurality of female contacts 5a is supported on the insulated holding plate 1 by means of a supporting plate 6, and the connection between each female contact 5a and each probe pin 2 is made with a leading wire (not shown). A male connector 7, having male contacts 7a, which can connect with the female contacts 5a, and a cable 8 tying up the leading wires, is connected with an inspection unit 9.
FIG. 2 indicates an example of the conventional inspection probe pin 2 comprising a conductive metallic tube 2a and a plunger 2b which is inserted into the tube 2a to act against a spring (not shown) so as to form a movable plunger 2b extending from the top of the tube 2a. A ring shaped salient 2c is provided around the top of the tube 2a. Each of the probe pins 2 is planted tightly on the insulated holding plate 1 by pushing the tube 2a into the holding opening 1a formed precisely on the holding plate 1 by means of NC machines (numerically controlled machines), or other suitable means.
FIG. 3 shows another example of the conventional probe pin 2 for inspection. The probe pin of FIG. 3 differs from the former example in that a salient 2d is provided at the outer surface of the top of the conductive metallic tube 2a. FIG. 4 indicates another example of a probe pin 13 for inspection formed by means of a plunger 13b being inserted into a conductive metallic tube 13a with a spring (not shown). The plunger 13b is movably projected from the top of the tube 13a. The pins 13 are insert into a slip-on socket 14 which is pushed into a holding opening 1a provided in plurality on an insulated holding plate 1, and a ring shaped salient 14a is formed around the top end of the slip-on socket 14 with the salient 14a being pushed into the holding opening 1a on the insulated holding plate 1.
However, as the conventional probe pin for inspection shown in FIG. 2 has the ring shaped salient 2c around the top end of the conductive metallic tube 2a, it is difficult to push the ring shaped salient 2c into the holding opening 1a precisely formed on the insulated holding plate 1 without bending or slanting the pins or crushing the ring shape salient. Moreover, the inner surface of the conductive metallic tube 2a may be deformed to prevent the plunger 2b from its movement.
The conventional probe pin 2 indicated in FIG. 3 suffers from the problem that when the salient 2d provided on outer surface of the top end of the conductive metallic tube 2a is pushed into the holding opening 1a, the installation position of the conductive metallic tube 1a is likely to deviate from the holding opening 1a, the diameter of which is precisely formed on the holding plate 1.
In the example described in FIG. 4, it is difficult to push the ring shaped salient 14a provided on outer surface of the top end of slip-on socket 14 for the probe pin 13 for inspection into the holding opening 1a formed on the insulated holding plate without slanting or bending the slip-on socket or crushing the ring shaped salient 14a to deform inner surface of the slip-on socket. As a result, it is difficult to remove a damaged probe pin 13.
In order to eliminate such problems, it will be easy to enlarge the holding opening 1a formed on the insulated holding plate, but the alignment will then become incorrect and the conductive metallic tube 2a or the slip-on socket forming the probe pin would easily come off from the holding opening 1a.
In order to prevent such a drawback, a shrinkable tube may be mounted on the projected portion of the conductive metallic tube 2a or the slip-on socket 14 from the lower surface of the insulated holding plate 1, or the conductive metallic tube 2a or the slip-on socket 14 may be fastened on the insulated holding plate with a bonding agent. These additional processes cause problems posing a more complex and costly operation.